The subject matter disclosed herein relates to rotary elements. More particularly, the subject matter disclosed herein relates to apparatuses and systems for reducing turbine rotational imbalance.
When disturbed from rest, all mechanical structures, such as turbomachine rotors, vibrate at particular frequencies. Rotational imbalances in the rotors exacerbate the vibrations, which can pose considerable problems when operating rotors, especially above certain rotational speeds. Excessive vibration can cause unnecessary fatigue, structural stress and strain, less efficient operation, or undesirable physical interference between moving parts, for example. Conventional balancing techniques attempt to adjust the weight of the rotor at a single speed, but these techniques cannot always compensate for rotor imbalances because often the imbalances arise or change while starting or operating the rotor. For example, asymmetric thermal heating of the rotor results in bending of the rotor shaft, which causes the rotor to be imbalanced around the rotational axis. In another example, the excitation coils of large turbo-generators sometimes shift along the rotor axis. If these shifts are not exactly symmetrical, mechanical stresses and strains are induced which also result in imbalances. Erosion of the compressor and turbine blades is a further mechanism that can unbalance a rotor of a large gas and steam turbine. These imbalances result from operation of the rotor, and hence, cannot be adequately addressed by conventional techniques.